The overall goal is to understand how synaptic pathways in the postnatal mammalian retina develop and to understand how this development is influenced by visual experience. Disruption of the normal sensory experience during development of young animals can lead to permanent defects in nervous tissue including the retina. Rearing animals in the dark "dark rearing" interferes with the normal sensory input to the retina and results in an alteration in the excitatory inputs onto the output neurons in the retina, the retinal ganglion cells. Using patch clamp techniques, the ratio of evoked synaptic mediated currents in the retinal ganglion cells will be examined in the retinas of both normal and dark reared retina. The alteration in excitatory inputs onto the retinal ganglion cells suggests that there are changes in the release properties of bipolar cells. Retinal ganglion cells receive input from bipolar cells, which release glutamate in response to photoreceptor activity. The release properties of bipolar cells will be characterized by using patch-clamp techniques to record evoked responses in retinal ganglion cells in normal and dark reared retina. The expression and localization of a protein responsible for transporting the excitatory neurotransmitter glutamate into synaptic vesicles of presynaptic terminals will be examined in developing retina, and in normal and dark reared retina. Characterization of the mechanisms involved in regulating synaptic activity in the developing retina is important baseline knowledge for understanding improper synaptic transmission in retinal dysfunction and disease.